- CNS therapy: All patients with initial CNS involvement undergo cranial radiotherapy for a total of 12 or 18 Gy. HR patients (precursor B-cell ALL with initial WBC count ≥ 200/nL and T-cell ALL with initial WBC count ≥ 100/nL) with no initial CNS involvement also undergo cranial radiotherapy for a total of 12 Gy, beginning 2-3 weeks after the last dose of HD cytarabine or clofarabine. LR patients and HR patients (precursor B-cell ALL with initial WBC count < 200/nL and T-cell ALL with initial WBC count < 100/nL) with no initial CNS involvement do not receive initial cranial radiotherapy. At the beginning of CNS therapy, before cranial radiotherapy, HR-I patients receive vincristine IV on day 1; doxorubicin hydrochloride IV over 24 hours on day 1; oral dexamethasone 3 times daily on days 1-7; and pegaspargase IV over 2 hours on day 7.